Sql Server Reporting Services Custom Assemblies

I'm not having an issue now - already solved it. I'm just posting here so someone else doesn't have to tear their hair out trying to figure out what the hell happened.

We have a custom DLL installed with SQL Reporting Services and functions called from reports. We recently added two optional parameters (VB) to one of the functions and the function stopped working from inside the reports. This was hard to track down since you don't get any error messages. Nothing in the event logs or the report services logs. Generally, these problems are related to security, so you start trying everything you can think of related to security.

It turns out, all we had to do was republish the reports. Apparently, when you publish the reports to the server, it looks at the custom assemblies and stores some info about the parameters. Who knew?